System for pressure-modulated shaping of the course of injection

ABSTRACT

A system for injecting fuel into the combustion chamber of a self-igniting internal combustion engine, has a control unit which acts upon a spring-controlled injection device which includes a nozzle needle, by way of which one or more injection openings are opened or closed. The control unit includes a first valve and a second valve, which each include one pressure chamber which communicate with one another via a pressure line. The first valve and the second valve are connected in series, and the first valve controls the subjection of the pressure chamber of the second valve to pressure, and the level of the injection pressure during the injection phases is controlled by the second valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 03/00013 filed onJan. 7, 2003.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

This invention relates to an improved system for pressure-modulatedshaping of the course of iniection of fuel into the combustion chamberof a self-igniting internal combustion engine. The term “course ofinjection” means the course of the fuel quantity, injected into thecombustion chamber, as a function of the crankshaft or camshaft angle.The essential variables are the duration of injection and the injectionquantity. These represent the course of injection in degrees ofcrankshaft angle, camshaft angle, or milliseconds, during which theinjection valves are opened and fuel reaches the interior of thecombustion chamber.

DESCRIPTION OF THE PRIOR ART

German Patent Disclosure DE 198 37 332 A1 relates to a control unit forcontrolling the pressure buildup in a pump unit. The control unit has acontrol valve and a valve actuating unit communicating with it. Thecontrol valve is embodied as an inward-opening valve in terms of theflow direction and has a valve body, disposed axially displaceably in ahousing of the control unit, that when the control valve is closed it isseated from the inside on a valve seat of the control valve. A throttleassembly is provided, by which the flow through the control valve, whenthe control valve is opened by a short stroke h, is throttled. With thecontrol valve opened by this stroke length, the valve seat is open as ithas been, but a further valve seat is closed, so that the pumped mediumhas to flow through the control valve via the throttle bores. Because ofthe thus-throttled flow through the control valve, a lesser pressure isbuilt up in a high-pressure region of the system. Conversely, when thecontrol valve is completely closed, both the first valve seat and thefurther valve seat are closed, thus disconnecting the bypass connection.The result is the buildup of a high pressure from the pump unit to thelow-pressure region of the system in the high-pressure region of thesystem.

German Patent Disclosure DE 42 38 727 A1 refers to a magnet valve. Themagnet valve serves to control the passage through a connection betweena high-pressure chamber, which is at least intermittently brought tohigh fluid pressure, and in particular a pump work chamber of a fuelinjection pump, and a low-pressure chamber. A valve body inserted into avalve housing and a bore in the valve body are provided; a valve closingmember in the form of a piston is displaceable in this bore by anelectromagnet, counter to the force of a restoring spring. The piston,beginning at a circular-cylindrical jacket face, tapers along a conicalface to a reduced diameter; with a conical high-pressure chambersurrounding the circular-cylindrical jacket face of the piston, theconical face cooperates with a communicating valve seat on the valvebody, which seat surrounds the reduced diameter of the piston. The coneangle of this seat is smaller than the cone angle of the conical face ofthe piston, and so the piston cooperates with the valve seat via asealing edge created at the transition between its cylindrical jacketface and the conical face. In the overflow direction from thehigh-pressure chamber to the low-pressure chamber, the sealing edge isfollowed by a throttle restriction that becomes operative at the onsetof the opening stroke. The throttle restriction is formed by athrottling segment in the area of overlap between the polygonal face ofthe piston and the valve seat face; the angle of the conical face of thepiston is slightly greater, preferably 0.5 to 1° greater, than the angleof the valve seat face, so that the flow cross section between theconical face of the piston and the valve seat face decreases steadilyover the entire circumference in the overflow direction to thelow-pressure chamber at the onset of the opening stroke. Because of thehigh flow velocities of the fuels between the injection phases—whetherthey are the preinjection, main injection or postinjection phases—withthis embodiment, cavitation damage can be prevented.

SUMMARY OF THE INVENTION

According to the present invention it is possible to control not onlythe control parameters of the injection onset, injection quantity,injection pressure, and number of injections, which in this connectionare considered to be conventional control parameters of a common railinjection system, but also the first phase of the injection event (theso-called “boot phase”) in terms of the length and the pressure level.Depending on the rpm and the load on the self-igniting internalcombustion engine, NO_(x) emissions can be affected quite favorably bymeans of the variation of the boot phase. The boot phase preceding themain injection serves to condition the mixture, to be converted duringthe main injection, in terms of an optimal or in other words as completeas possible combustion, with an optimal exhaust gas composition.

The possibility of influencing the boot phase in terms of its duration,independently of the control parameters of injection onset, injectionquantity and injection pressure and so forth, makes it possible to adaptthe course of injection to the fuel used during the boot phase as well.In stationary Diesel engines, or Diesel engines for driving ships, heavyoil is often used as fuel, whose atomization behavior compared to Dieseloil, which is injected into the combustion chambers of passenger carDiesel engines, is substantially poorer. Preparing the mixture by meansof a controlled injection of fuel makes better preparation of thecompressed mixture possible in a way that is independent of the fuelquality, so that during the combustion phase in the combustion chamber,favorable conditions are established in terms of emissions. Especiallyadvantageously, the more-favorable NO_(x) emissions can thus be attainedfor the same fuel consumption of the engines. This concept also makes itpossible for multiple injections (preinjection phases) for the sake ofpreheating the mixture and a postinjection phase for reducing the smokevalue to be combined with shaping of the course of injection.

The proposed invention moreover takes the use of heavy oil as a fuel forDiesel engines into account by providing that the actuating devices,such as magnet coils of electromagnets or piezoelectric actuators withhydraulic boosters, are separated from the fuel by diaphragms. Thediaphragms for instance shield the armature plates and magnets from thefuel, which to improve its flow properties may be heated to temperaturesof up to 140° C. and more.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in further detail below in conjunction withthe drawings, in which:

FIG. 1 is a sectional view of a control assembly with a series-connectedcombination of one 3/2-way valve and one 2/2-way valve;

FIG. 2, the control assembly of FIG. 1, secured to a high-pressurecollection chamber (common rail);

FIG. 3, the control assembly of FIG. 1, associated directly with aninjector (nozzle holder combination);

FIG. 4, a variant embodiment of the control assembly of FIG. 1 in splitform, in which one part of the control assembly is associated with thecommon rail and the other part of the control assembly is associatedwith the injector (nozzle holder combination);

FIGS. 5.1 and 5.2 show the courses of the nozzle needle stroke and theinjection pressure, each plotted on the time axis;

FIG. 5.3 shows various triggering times of a 3/2-way valve;

FIG. 5.4, the triggering time of a 2/2-way valve that makes the fullpressure buildup possible;

FIG. 6, the courses of the pressure, needle stroke, and triggering timesof a 3/2-way valve and a 2/2-way valve; and

FIG. 7, the courses of the pressure, needle stroke, and triggering timesof a 3/2-way valve and a 2/2-way valve in the case of multipleinjection, combined with boot rate shaping.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a control assembly with a series-connected combination ofone 3/2-way valve and one 2/2-way valve. The control unit 6 is actedupon by fuel that is at high pressure via a common rail or otherhigh-pressure source. The control unit 6 includes a pressureless outlet3 and an outlet 2 on the high-pressure side. The control unit 6 is ofmodular construction and includes an upper part 7, in which a firstactuating device 4 and a second actuating device 5 are received next toone another. Located below the upper part 7 of the control unit 6 is amiddle part 8, which is adioined by a lower part 9.

The control unit 6 that can be seen in FIG. 1 is acted upon by fuel thatis at high pressure via a common rail or other high-pressure source. Thecontrol unit 6 includes a pressureless outlet 3 and an outlet 2 on thehigh-pressure side. The control unit 6 is of modular construction andincludes an upper part 7, in which a first actuating device 4 and asecond actuating device 5 are received next to one another. Locatedbelow the upper part 7 of the control unit 7 is a middle part 8, whichis adjoined by a lower part 9.

The control unit 6 includes a first valve 10 and a second valve 11. Thefirst valve 10 is embodied as a 3/2-way valve, whose pressure chamber 28is acted upon by fuel at high pressure via the high-pressure inlet 1. Incomparison, the second valve 11 is embodied as a 2/2-way valve. Thefirst valve 10 is controlled by the first actuating device 4, which inthe view of FIG. 1 is designed as an electromagnet. The magnet coil 13of the electromagnet is received in the upper part 7 of the control unit6. An actuation assembly 21, 22 for pressure relief of a control chamber24 of the first valve 10 acts upon a closing element 20, which in turnopens or closes an outlet throttle 23 for pressure relief of the controlchamber 24 of the first valve 10. In the variant embodiment of thecontrol unit 6 shown in FIG. 1, the first actuating device 4 is embodiedas an electromagnet. Alternatively, it is possible to embody the firstactuating device 4 as a piezoelectric actuator, which to increase theadjustment distance can be followed by a hydraulic booster. Theactuating assembly 21, 22—embodied in the view of FIG. 1 as an armatureplate 21 and a peg 22 joined to it—is acted upon via a restoring spring12, which keeps the armature plate 21 of the actuating assembly 21, 22at a distance from the lower end face of the magnet coil 13 of the firstactuating device 4. The shaft 22 of the actuating assembly 21, 22includes a contact face 19, which partly surrounds the closing element20 that here is embodied spherically and presses it into the seat insidethe middle part 8 that closes the outlet of the control chamber 24.Reference numeral 18 indicates the line of separation between the upperpart 7 and middle part 8, and defines a stop face.

Below the first actuating device 4, a first hollow chamber 15 isembodied in the upper part 7 of the control unit 6 and serves to receivethe armature plate 21 of the actuating assembly 21, 22. In the regionabove the parting joint of the upper part 7 and the middle part 8 of thecontrol unit 6, the first hollow chamber 15 is sealed off from the entryof fuel by means of a flexible diaphragm element 17. When the controlunit 6 is used with large Diesel engines, of the kind used for instanceas stationary Diesel engines or for driving ships, heavy oil is used asfuel, which is preheated to temperatures of up to 140° C. and more inorder to improve its flow properties. To protect the first actuatingdevice 4—and analogously the second actuating device 5, which actuatesthe second valve 11—against damage and the entry of viscous fuel, thefirst hollow chamber 15 and analogously the second hollow chamber 16 ofthe second actuating device 5 are protected against the entrance of hotfuel by means of flexible diaphragm elements 17 in the region of theparting joint to the middle part 8 of the control unit 6.

The control quantity diverted upon pressure relief of the controlchamber 24 of the first valve 10, which is preferably embodied as a3/2-way valve, enters into the annular chamber surrounding the shaft 22of the actuating assembly 21, 22 and flows from there into an overflowbore 25 extending horizontally in the middle part 8. From thehorizontally extending overflow bore 25 in the middle part 8 of thecontrol unit 6, both an overflow bore 26 extending in the verticaldirection in the middle part 8 and an outflow line 34 branch off. Viathe outflow line 34, the diverted fuel volume, flowing out of thecontrol chamber 24, can be introduced into the pressureless outlet 3,from which the diverted fuel volume flows back into the fuel tank.

The first valve 10 includes a valve body 27, whose upper face enddefines the control chamber 24. The control chamber 24 is furthermoredefined by the lower part 9 of the control unit 6 and a portion of thelower face of the middle part 8 of the control unit 6 in which portionthe outlet throttle 23 is accommodated that can be opened and closed bythe closing element 20, configured spherically in this case.Furthermore, in the region surrounded by the annularly configuredpressure chamber 28, the valve body 27 of the first valve 10 includes aninlet throttle restriction 30, which communicates with a longitudinalbore that discharges at the upper face end of the valve body 27. Via thehigh-pressure inlet 1, the inlet throttle restriction 30 and theaforementioned longitudinal bore, shown in dashed lines in FIG. 1, it isassured that the control chamber 24 of the first valve 10 is constantlysubjected to a control pressure. Furthermore, the valve body 27 of thefirst valve 10 includes a conical seat 29 that cooperates with acorresponding seat face of the lower part 9. In FIG. 1, the conical seat29 of the valve body 27 has moved into a seat face, corresponding to it,of the lower part 9 of the control unit 6 and closes off both thepressureless outlet 3 and the transverse bore 32, branching offunderneath the annularly extending pressure chamber 28, to the pressurechamber 36 of the second valve 11, which is preferably embodied as a2/2-way valve. The valve body 27 of the first valve 10 furthermoreincludes an extension 31, which is disposed below the conical seat 29and closes or opens the pressureless outlet 3 in accordance with thestroke length of the valve body 27 in the lower part 9 of the controlunit 6. Upon applying current to the first actuating device 4, thecontrol chamber 24 is pressure-relieved, and accordingly the valve body27 moves vertically upward until its upper face end contacts the stopface 18 of the middle part 8. In accordance with this vertical strokemotion, the conical seat 29 moves out of its seat face in the lower part9 of the control unit 6, and the extension 31 moves partway into thebore adjoining the pressure chamber 28, precisely far enough that, viathe annular pressure chamber 28, the high-pressure inlet 1 and thetransverse bore 32 that acts upon the pressure chamber 36 of the secondvalve 11 are supplied with high pressure.

The second actuating device 5, likewise accommodated in the upper part 7of the control unit 6 and likewise embodied as a magnet valve in thevariant embodiment of FIG. 1, actuates a valve body 35 of the secondvalve 11. Below the magnet coil 13 of the second actuating device 5,there is a second hollow chamber 16 embodied in the upper part 7; it isprotected against the inflow of preheated fuel via the diaphragm element17. If fuel were to flow in and then cool down, given the short strokelengths and the adjusting travel distances or lengths that theelectromagnet requires to actuate the first valve 10 and the secondvalve 11, operation with the requisite precision would no longer befeasible if preheated heavy oil were used as fuel, which is quite usualin stationary large Diesel motors as well as in Diesel motors used todrive ships.

The pressure chamber 36 of the second valve 11, acted upon via thetransverse bore 32, discharges into a high-pressure outlet 2, which isin communication with a nozzle chamber, not shown in FIG. 1, aninjection device, such as a nozzle holder combination or an injector. Aconical seat 39 is embodied on the end of the valve body 35 of thesecond valve 11 pointing toward the high-pressure outlet 2 andcooperates with a corresponding seat face in the lower part 9 of thecontrol unit 6. In the lower region of the valve body 35, a throttlerestriction 37 is embodied, which communicates with the pressure chamber36 and with a longitudinal bore 38 inside the valve body 35.

Both the first actuating device 4 and the second actuating device 5 aretriggered by means of a triggering part 40, which communicates viatriggering lines 14 with the magnet coils 13 of the first actuatingdevice 4 and second actuating device 5, respectively.

The mode of operation of the variant embodiment shown in FIG. 1 is asfollows:

The valve body 27 of the hydraulic 3/2-way valve 10 is controlled bymeans of the first actuating device 4, embodied as an electromagnet. Theopening and closing of the valve body 27 is controlled by the pressurerelief of the control chamber 24 via the first actuating device 4. Thepressure drop or pressure rise is independent of the diameters of theinlet throttle restriction 30 in the lower part of the valve body 27 andof the design of the outlet throttle 23 above the control chamber 24. Ifno current is supplied to the magnet coil 13 of the first actuatingdevice 4, the valve body 27, by movement of its conical seat 29 into thecorresponding seat face inside the lower part 9 of the control unit 6,closes off the high-pressure inlet 1 via the transverse bore 32 to thepressure chamber 36 of the second valve 11. The high-pressure outlet 2of the second valve 11, in this state, communicates with thepressureless outlet 3 below the first valve 10. By way of outlet 3, thecontrol volume quantity diverted from the control chamber 24 in itspressure relief also flows to the low-pressure side of the control unit6 via the horizontally extending overflow bore 25 or the outflow line34. In this state, a nozzle needle of an injection device remainsclosed; see FIGS. 2 and 3. Upon the activation of the first actuatingdevice 4 initiated via the triggering part 40, that is, upon excitationof the magnet coil 13, the valve body 27 is moved as far as the stop 18.By inward motion, effected in accordance with the stroke length, of theextension 31 into the bore adjoining the pressure chamber 28 underneath,a closure of the pressureless outlet 3 ensues; the high-pressure inlet 1communicates via the pressure chamber 28 with the pressure chamber 36 ofthe second control valve 11. The onset of the injection event nowoccurs. The injection pressure is controlled via the second actuatingdevice 5, which actuates the valve body 35 of the second valve 11 andwhose magnet coil is activated by the triggering part 40 via atriggering line 14. In the closed state of the second valve 11, that is,when the magnet coil 13 of the second actuating device 5 is notactivated, the inlet to the injection nozzle is throttled via thethrottle restriction 37 embodied in the valve body 35. With thetriggering sequence described, that is, a supply of current to themagnet coil 13 of the first actuating device 4 and an ensuing pressurerelief of the control chamber 24, it is true that the high-pressureinlet 1 is indeed in communication with the pressure chamber 36 of thesecond valve 11 via the pressure chamber 28 and the transverse bore 32,but in this phase of the injection only a throttled action by thehigh-pressure inlet 2 on the injection nozzle occurs (see theillustration in FIG. 2). As a function of the actuation of the secondactuating device 5 via the triggering part 40, an unthrottled action onthe nozzle holder combination 56 (see the illustration in FIG. 2) forthe nozzle chamber 59 can be done depending on the triggering, that is,on the stroke length of the valve body 35 of the second valve 11 insidethe lower part 9 of the control unit 6. Upon opening of the second valve11, the injection nozzle at the nozzle holder combination (see FIGS. 2and 3) communicates unthrottled with the high pressure source via thehigh-pressure inlet 1, the pressure chamber 28 of the first valve 10,the transverse bore 32, and the pressure chamber 36 of the second valve11. For termination of the injection, the high-pressure outlet 2 leadingto the nozzle holder combination or to the injector 56 (see theillustration in FIG. 2) is opened by actuation of the valve body 27 ofthe first valve 10, preferably embodied as a 3/2-way valve, that is, bymovement of the conical seat 29 into the seat face located in the lowerpart 9, as a result of which the high-pressure outlet 2 along with thepressureless outlet 3 is pressure-relieved for pressure relief of thedevice for injecting fuel 56. After that, via the restoring spring 12,which is received by the magnet coil 13 surrounded in the upper part 7of the control unit 6, valve 11 is closed.

FIG. 2 shows the control unit of FIG. 1, secured to a high-pressurecollection chamber (common rail). As illustrated, the control unit 6 isrepresented only by its upper part 7, middle part 8, and lower part 9.The common rail 50 is configured essentially in tubular form. Along abutt joint 51, the common rail 50 and the control unit 6 communicatewith one another. Above the control unit 6, the triggering lines 14 ofthe first actuating device 4 and of the second actuating device 5 in theupper part of the control unit 6 are shown, by way of which the magnetvalves for actuating the first valve 10 and the second valve 11 aretriggered by means of the triggering part 40.

The common rail 50 communicates with the tank 55 via a forward fuel flow53 and includes a high-pressure fuel pump 52, which brings the fuel fromthe tank 55 to an arbitrary pressure level, for instance between 600 and1800 bar.

The pressureless outlet 3 at the control unit 6 likewise communicateswith the tank 55, via a return line 54, so that the fuel quantitydiverted from the control chamber 24 of the first valve 10 can return tothe fuel reservoir again. Subjection of the pressure chamber 36 of thesecond valve 11 to pressure causes high pressure to prevail at thehigh-pressure outlet 2 of the control unit 6, and in accordance with thefurther course of the high-pressure outlet 2 this pressure also prevailsat the nozzle chamber 59 of the nozzle holder combination 56. Referencenumeral 56 indicates a nozzle holder combination which includes a nozzleneedle 58, which is subjected to a compression spring inside the nozzleholder combination 56. Depending on the pressure to which the nozzlechamber 59 is subjected, injection openings 57 disposed on the endtoward the combustion chamber of the nozzle holder combination 56 aresupplied with fuel or closed. Via a further pressureless outlet 60, thespring chamber of the nozzle holder combination 56 communicates with thereturn flow 54 to the fuel tank 55, so that excess fuel volume canlikewise flow back into the tank 55. In the illustration in FIG. 2, thecontrol unit 6 is associated directly with the common rail 50, and as aresult a short structural length of the high-pressure inlet 1 from thecommon rail 50 to the control unit 6 can be achieved.

The illustration in FIG. 3 shows the control unit of FIG. 1, which isdisposed directly above an iniector (nozzle holder combination). Thisintegrated version, identified by reference numeral 70, of a controlunit 6 in the upper region of a nozzle holder combination 56 or of somedifferently configured device for injecting fuel into the combustionchambers of a self-igniting internal combustion engine, is triggeredanalogously to what is shown in FIG. 2 via triggering lines 14 by meansof a triggering part 40. Analogously to what FIG. 2 shows, the commonrail 50 is subjected via a high-pressure fuel pump 52 to a fuel volumeat high pressure, which the high-pressure fuel pump 52 in turn pumps outof the tank 55 via a forward flow 53. A pressureless outlet 60 of thedevice 56 for injecting fuel, here embodied as a nozzle holdercombination, discharges into the tank 55. From the pressureless outlet 3of the control unit 6, which in the variant embodiment of FIG. 3discharges into the spring chamber of the nozzle holder combination 56,the leak fuel volume flows back to the tank 55, via the pressurelessoutlet 60 and the return flow 54. As a result of the integrated version70 of the control unit 6 above a device 56 for injecting fuel, anespecially short high-pressure outlet 2 is advantageously obtained, byway of which the nozzle chamber 59 that surrounds the nozzle needle 58can be acted upon by high pressure. In its integrated version 70 aswell, the control unit 6 has an upper part 7, the middle part 8, and thelower part 9, this last part receiving both the first valve 10 and thesecond valve 11, the latter not shown in FIG. 3.

FIG. 4 shows a variant embodiment of the control unit in split form, inwhich one part of the control unit is associated directly with thecommon rail and the other part of the control unit is associateddirectly with the injector.

The variant embodiment of the control unit 6 in split form is identifiedby reference numeral 80. In this variant embodiment, the control unit 80includes two components, and the first valve 10 and the first actuatingdevice 4 that actuates it are received in the upper part 7.1, the middlepart 8.1, and the lower part 9.1. The common rail 50 communicatesdirectly with the lower part 9.1 of the control unit 80. From the lowerpart 9.1 of the split control unit 80, that is, from the pressurechamber 28 of the first valve 10, a connecting line 81 branches off, byway of which the pressure chamber 36 of the second valve 11, which iscontained in the second part of the split embodied control unit 80, isacted upon by fuel that is at high pressure.

The second valve 11, preferably embodied as a 2/2-way valve, isaccommodated in the upper part 7.2, middle part 8.2, and lower part 9.2of the variant embodiment of the control unit 80 in split form. Thehigh-pressure outlet 2, which subjects the nozzle chamber 59 of thenozzle holder combination 56 to high pressure, branches off from thepressure chamber 36 of the second valve 11. In accordance with thestroke motion of the nozzle needle 58 counter to the springprestressing, the injection openings 57 on the end toward the combustionchamber of the nozzle holder combination 56 are either subjected to fuelor closed. Reference numeral 60 indicates a pressureless outlet, by wayof which excess fuel volume flows back into a tank, not shown here.

FIGS. 5.1 and 5.2 show the courses of the nozzle needle stroke and theinjection pressure, each plotted over the time axis.

In the graph in FIG. 5.1, the needle stroke length 23 can be seenplotted over the time axis 84. As can be seen from FIG. 5.1, with theembodiment proposed according to the invention, both short boot phases87 and intentionally longer boot phases 88 can precede a main injection90. The curves in FIG. 5.2 show the pressure level 92 which is attainedduring the boot phase 86 preceding the main injection 90, whether it isdimensioned as a short boot phase 87 or a long boot phase 88. Thepressure level 92 during the boot phase 86 is adjustable with thethrottle 37 shown in FIG. 1 in proportion to the system pressure 91,that is, the maximum pressure and is dependent on the through stroke andthrottle size.

In comparison to the pressure level 89 prevailing during the maininjection phase 90, in which the maximum level prevails, the injectionpressure during the boot phases 86 proceeds at a lower pressure level92. Within the boot phase, a small quantity of fuel comes to be injectedinto the combustion chamber; this serves essentially to improve theturbulence of the compressed air inside the combustion chamber, and itspurpose is conditioning the air mixture to bring about an ensuingoptimal combustion during the main injection phase 90. The course of themain injection phase 90 is characterized by a pressure maximum 89, adescending pressure edge 93 and a steeply rising pressure edge 94 at theonset of the main injection phase 90. The maximum pressure level 91established during the main injection phase 90 is essentially equivalentto the pressure maximum 89 that is established inside the common rail50.

FIG. 5.3 shows various triggering times of a 3/2-way valve, which definethe injection pressure course and the injection quantity.

Reference numeral 95 marks a first injection onset of the first valve10, which is designed as a 3/2-way valve, while reference numeral 103identifies the end of a first injection pressure course 98. The firstinjection onset 95 is tripped by the triggering instant, or time, of theelectromagnet 13 that triggers the first valve 10. Depending on thetriggering time, a second injection onset 96 and a third injection onset97 can also be defined, as a result of which—while keeping the end ofinjection 103 unchanged—injection pressure courses 98, 99, 100 ofvarious lengths can be achieved, and by means of them the quantity offuel delivered to the combustion chamber of an internal combustionengine is determined.

The pressure level that is reached upon triggering of the first valve 10by the electromagnet 13 is identified by reference numeral 101.

FIG. 5.4 shows the triggering time of the second valve 11, which isembodied as a 2/2-way valve. This valve is opened by the electromagnet13 at time 102 and closed by the electromagnet at time 103. During theperiod of time identified by reference numeral 100, both valves areopen, so that during this phase, the pressure maximum 89 of FIG. 5.3 isestablished, at which the two pressure levels 101 and 105 at the 3/2-wayvalve and at the 2/2-way valve, respectively, that is, at the firstvalve 10 and second valve 11, are superimposed on one another. Dependingon the triggering time 90, the boot phase 86 preceding the maininjection phase 50 can be shaped as a short boot phase 87 or a long bootphase 88, in which the first pressure level 101 applied upon opening ofthe first valve 10 embodied as a 3/2-way valve prevails.

If as in FIG. 4 the first valve 10 and the second valve 11 are openedand closed simultaneously, as indicated by the curve course 104, then amain injection without a preceding boot phase 86 as in FIG. 5.2 isestablished.

FIG. 6 shows the courses of the pressure and needle stroke and thetriggering times of a 3/2-way valve and a 2/2-way valve, in multipleinjection with boot rate shaping.

In FIG. 6, the aforementioned parameters are shown relative to the topdead center (O.T.) 106 of a piston in the cylinder of an internalcombustion engine. It can be seen from the upper curve course in FIG. 7that a preinjection 108 and a postinjection 109 are both associated witha main injection phase 90 with a preceding boot phase 86. During thepreinjection 108, the nozzle needle, which for instance represents theinjection valve member of an injector, is partway open, represented byreference numeral 110; during the period of time indicated by referencenumeral 111, the nozzle needle is completely open, in accordance withthe course 83 of the needle stroke length in FIG. 7. With the 2/2-wayvalve 11, the length of the boot phase 86 can be controlled insynchronism with the first valve 10 upon changes in the injection onset.

During the preinjection 108, the first valve 10, embodied as a 3/2-wayvalve, is briefly opened for the duration 112 and is then closed again,as a result of which a slight quantity of fuel for preconditioning isinjected into the combustion chamber of the engine. At the time markedby reference numeral 95, the 3/2-way valve opens for the duration of themain injection phase 113 and closes again at time 103. During thepostinjection phase 109, the 3/2-way valve, that is, the first valve 10,is opened for the duration 114. The 2/2-way valve, that is, the secondvalve 11, is opened at time 116 and not closed again until time 117,times that are shifted relative to the opening time 95 and closing time103 of the first valve 10; in the shifted opening duration course of the2/2-way valve 115 shown in FIG. 7, this closing time can coincide withthe end of the postinjection phase 114.

As a result of the shift in the opening and closing times 116 and 117,respectively, of the 2/2-way valve, that is, the second valve 11, bootrate shaping can be achieved; that is, the course of the injectionpressure, and thus the injection quantity, can both be shaped inaccordance with predetermined conditions and criteria. From the curvecourses shown in FIG. 7, it can also be seen that a main injection phase90, either with or without a boot phase 86, can be preceded and followedby both a preinjection 108 and a postinjection 109.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

1. In a system for injecting fuel into the combustion chamber of aself-igniting internal combustion engine, having a control unit (6, 80),which acts upon a spring-controlled injection device (56) which includesa nozzle needle (58), the control unit (6, 80) including a first valve(10) and a second valve (11), which each include one pressure chamber(28, 36) which communicate with one another via a pressure line (32,81), the improvement wherein the first valve (10) and the second valve(11) are connected in series, and the first valve (10) controls thesubjection of the pressure chamber (36) of the second valve (11) topressure, and the level (91, 92) of the injection pressure during theinjection phases (86, 87, 88; 90) is controlled by the second valve(11), wherein the second valve (11), which can be acted upon via thefirst valve (1O), is embodied as a 2/2-way valve, from whose pressurechamber (36) a high-pressure outlet (3) extends to the nozzle chamber(59) of the injection device (56), and wherein the second valve (11)comprising a valve body (35) including a conical seat (39) above which athrottle restriction (37) is disposed that communicates with alongitudinal bore (38) pointing toward the high-pressure outlet (2). 2.The system for injecting fuel of claim 1, wherein the control unit (6,80) comprises actuating devices (4, 5) for the first valve (10) and thesecond valve (11), which actuating devices are each separated from thefuel via a respective diaphragm element (17).
 3. The system forinjecting fuel of claim 2, wherein the diaphragm elements (17) arereceived on an upper part (7, 7.1, 7.2) of the control unit (6) above aparting joint to a middle part (8, 8.1, 8.2) of the control unit (6,80).
 4. The system for injecting fuel of claim 1, wherein the controlunit (6, 80) is received on the common rail (50).
 5. The system forinjecting fuel of claim 1, wherein the control unit (6) is disposeddirectly above the injection device (56).
 6. The system for injectingfuel of claim 1, wherein the control unit (80) is embodied in splitform, and wherein one part (7.1, 8.1, 9.1) receiving the first valve(10) is on the common rail (50), and the part (7.2, 8.2, 9.2) receivingthe second valve (11) is associated with the injection device (56). 7.The system for injecting fuel of claim 6, wherein the pressure chambers(28, 36) of the first valve (10) and the second valve (11) communicatevia a line connection (81).
 8. The system for injecting fuel of claim 1,further comprising one control unit (6, 80) and one injection device(56) assigned to each cylinder of a self-igniting internal combustionengine.
 9. In a system for injecting fuel into the combustion chamber ofa self-igniting internal combustion engine, having a control unit (6,80), which acts upon a spring-controlled injection device (56) whichincludes a nozzle needle (58), the control unit (6, 80) including afirst valve (10) and a second valve (11), which each include onepressure chamber (28, 36) which communicate with one another via apressure line (32, 81), the improvement wherein the first valve (10) andthe second valve (11) are connected in series, and the first valve (10)controls the subjection of the pressure chamber (36) of the second valve(11) to pressure, and the level (91, 92) of the injection pressureduring the injection phases (86, 87, 88; 90) is controlled by the secondvalve (11), and wherein the first valve (10) is a 3/2-way valve, whosepressure chamber (28) is acted upon via a hi2h-pressure inlet (1), andwherein both a closable, pressureless outlet (3) and the pressure line(32, 81) branch off underneath the pressure chamber (28), and whereinthe first valve (10) comprises a valve body (27) having a conical seat(29) which closes both the pressure line (32) and the pressurelessoutlet (3), and wherein the valve body (27) comprises an inlet throttle(30), which communicates via a conduit with a control chamber (24) thatcan be pressure-relieved by an actuating device (4).
 10. The system forinjecting fuel of claim 9, further comprising an overflow bore (25) andan outflow line (34), whereby a control quantity, diverted via an outletthrottle (23) upon pressure relief of the control chamber (24), isdiverted into the pressureless outlet (3).
 11. In a system for injectingfuel into the combustion chamber of a self-igniting internal combustionengine, having a control unit (6, 80), which acts upon aspring-controlled injection device (56) which includes a nozzle needle(58), the control unit (6, 80) including a first valve (10) and a secondvalve (11), which each include one pressure chamber (28, 36) whichcommunicate with one another via a pressure line (32, 81), theimprovement wherein the first valve (10) and the second valve (11) areconnected in series, and the first valve (10) controls the subjection ofthe pressure chamber (36) of the second valve (11) to pressure, and thelevel (91, 92) of the injection pressure durin2 the injection phases(86, 87, 88; 90) is controlled by the second valve (11), and wherein thefirst valve (10) is a 3/2-way valve, whose pressure chamber (28) isacted upon via a high-pressure inlet (1), and wherein both a closable,pressureless outlet (3) and the pressure line (32, 81) branch offunderneath the pressure chamber (28), and wherein the first valve (10)comprises a valve body (27) having a conical seat (29) which closes boththe pressure line (32) and the pressureless outlet (3), and wherein thevalve body (27) includes an extension (31), which closes and opens thepressureless outlet (3) as a function of the stroke length of the valvebody (27), wherein the extension (31) extends from the conical seat. 12.In a system for injecting fuel into the combustion chamber of aself-igniting internal combustion engine, having a control unit (6, 80),which acts upon a spring-controlled injection device (56) which includesa nozzle needle (58), the control unit (6, 80) including a first valve(10) and a second valve (11), which each include one pressure chamber(28, 36) which communicate with one another via a pressure line (32,81), the improvement wherein the first valve (10) and the second valve(11) are connected in series, and the first valve (10) controls thesubjection of the pressure chamber (36) of the second valve (11) topressure, and the level (91, 92) of the injection pressure during theinjection phases (86, 87, 88; 90) is controlled by the second valve(11), and wherein the first valve (10) is a 3/2-way valve, whosepressure chamber (28) is acted upon via a high-pressure inlet (1), andwherein both a closable, pressureless outlet (3) and the pressure line(32, 81) branch off underneath the pressure chamber (28), and whereinthe first valve (10) comprises a valve body (27) having a conical seat(29) which closes both the pressure line (32) and the pressurelessoutlet (3), and wherein the stroke length of the valve body (27) of thefirst valve (10) is defined by a stop face (18), which is formed by amiddle part (8) of the control unit (6, 80).